docs: def get_axis_variables(ds):
      '''
      Returns a list of variables that define an axis of the dataset
  
      :param netCDF4.Dataset ds: An open netCDF4 Dataset
      '''
      axis_variables = []
      for ncvar in ds.get_variables_by_attributes(axis=lambda x: x is not None):
          axis_variables.append(ncvar.name)
      return axis_variables